Whooping cough, caused by Bordetella pertussis, is presently one of the ten most common causes of death from infectious disease worldwide. Patients first present with a common cold and a cough. However, the disease progresses to paroxysmal coughing followed by a characteristic inspiratory whoop. Secondary symptoms arising from bacterial pneumonia, neurological complications (i.e., seizures and encephalopathy), and pressure effect complications (i.e., pneumothorax, epistaxis, subdural hematomas, hernias, and rectal prolapse) can also occur. From the onset of initial symptoms, the disease can take 6-8 weeks to resolve. Bordetella parapertussis is closely related to B. pertussis and may cause a similar illness, especially in children; however, the symptoms are less severe and are generally of shorter duration than B. pertussis. 
Pertussis and its associated complications were a major cause of infant and childhood mortality until the introduction of the diphtheria-tetanus-pertussis (DTP) vaccine in the 1940s. Widespread use of the vaccine in the American population resulted in a 98% decrease in the incidence of pertussis. According to the Centers for Disease Control (CDC; Atlanta, Ga.), there has been a resurgence of pertussis, and the incidence of pertussis in the general population has been on the rise since 1991. There was an 82% increase in total cases reported to the CDC in 1993 compared to the same period in 1992 (1992=3004; 1993=5457). In 1992, there were outbreaks of pertussis in Massachusetts and Maryland, and in 1994 there was an outbreak of erythromycin-resistant B. pertussis described in Arizona. This trend is also being seen outside the United States. In 1996, the Netherlands had an outbreak of pertussis, reporting 12 times the number of cases seen in 1995 (1995=341; 1996=4231).
Many cases of B. pertussis go undiagnosed and unreported. While pertussis is highly communicable and can cause severe disease, symptoms in older children and adults, including those previously immunized, may be difficult to differentiate from the nonspecific symptoms of bronchitis and upper respiratory tract infections. Clinical diagnosis of pertussis is complicated by the fact that the characteristic cough (whoop) is rarely observed in infants and adult patients.